How did the worst language learners in Europe get promoted to be in charge of foreign language learning?
Because we're the biggest travellers in the English speaking world, and generally most learners outside South Korea, South America, the Philippines and to a point, Saudi Arabia.prefer standard English to American English.
Coming from the country that the language is named after is of course also far from a hindrance.
I think there is a time and place for classes with no use of the local language
There's certainly a place. Even very many places since most language learning (where English is concerned) is enabled by teachers who do not speak the students' L1. In fact in one of the thousands of classes that happen daily where the students are from different countries, the teacher would have to be a pretty exceptional polyglot.
When I first started teaching English back in the UK, I had a class with students from Japan, China, Syria, Turkey, Russia, and Poland, and when I worked onboard the ship I had classes with learners from the Philippines, Borneo, Russia, Romania, Croatia, France, Italy and Poland too, all in the same class.
Taiwan has never struck me as a center of good foreign language learning
The same, however it has one hell of a lot of language schools, a ruthless commercial market and a decided preference for teachers who don't speak Chinese.
I'd also guess that of all those who've taught in Poland, only a minority of us speak Polish well enough to hold a good conversation in it.